The proposed research deals with the elucidation of the biochemistry of DNA replication. Our recent work is focused on two main topics: factors involved in DNA chain elongation and the mechanism of DNA chain initiation. DNA chain elongation will be examined by studying the requirement for factors that affect the following parameters: template-primer binding, nucleotide addition, dissociation and reassociation of DNA polymerase during synthesis and ability to propagate chains past secondary structure in the template. All of the above steps in elongation can be shown to be rate-limiting for synthesis. We have devised an experimental system that measures the above. The factors to be tested along with DNA polymerase III of E. coli are elongation factors I (Co-Pol) and II and DNA binding protein. DNA chain initiation will be studied with a system capable of synthesizing double-stranded DNA from single-stranded phiX174 DNA. We have isolated a "complex" that can attach to DNA and is capable of RF formation and is specific for phiX174 DNA. It synthesizes DNA chains synchronously and can be readily studied (i. e., what the primer is). BIBLIOGRAPHIC REFERENCES: Molineux, I.J. and Gefter, M.L. (1975). Properties of the Escherichia coli DNA-Binding (Unwinding) Protein Interaction with Nucleolytic Enzymes and DNA. J. Mol. Biol., in press. Molineux, I.J., Pauli, A., and Gefter, M.L. (1975). Physical Studies of the DNA-DNA Binding Interactions. J. Mol. Biol., in press.